issue#1
alexander@alexander-X240:~/ros/dev_ws$ sudo rosdep init
ERROR: cannot download default sources list from:
https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list
Website may be down.
solu1(recommand solu2):   

  download from  https://raw.githubusercontents.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list
             to /etc/ros/rosdep/sources.list.d/20-default.list
solu2:   
modify the following file, change   raw.githubusercontent.com to  raw.githubusercontents.com
•/usr/lib/python2.7/dist-packages/rosdep2/gbpdistro_support.py
•/usr/lib/python2.7/dist-packages/rosdep2/rep3.py
•/usr/lib/python2.7/dist-packages/rosdistro/__init__.py
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原文链接：https://blog.csdn.net/weixin_42584917/article/details/114448355

issue#2
alexander@alexander-X240:~/ros/dev_ws$ rosdep update
reading in sources list data from /etc/ros/rosdep/sources.list.d
Hit https://raw.githubusercontents.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml
Hit https://raw.githubusercontents.com/ros/rosdistro/master/rosdep/base.yaml
Hit https://raw.githubusercontents.com/ros/rosdistro/master/rosdep/python.yaml
Hit https://raw.githubusercontents.com/ros/rosdistro/master/rosdep/ruby.yaml
ERROR: unable to process source [https://raw.githubusercontents.com/ros/rosdistro/master/releases/fuerte.yaml]:
    Failed to download target platform data for gbpdistro:
    <urlopen error [Errno 104] Connection reset by peer>
Query rosdistro index https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml
ERROR: error loading sources list:
    <urlopen error <urlopen error timed out> (https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml)>

solu:  

same as solue2@issue#1

reference:
https://blog.csdn.net/qq_30267617/article/details/115028689?utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1.no_search_link&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1.no_search_link
https://blog.csdn.net/weixin_42584917/article/details/114448355